Folded optical systems

ABSTRACT

Single fold optical systems that include a power prism and a lens stack including two or more refractive lens elements. The single fold optical system may provide a long mechanical back focus without increasing the Z-height of the optical system. Providing power on the prism may reduce the optical total length and reduce the X-length of the optical system. The single folded optical systems may provide reduced Z-axis height and reduced X-axis length when compared to conventional double folded optical systems with similar optical characteristics. In addition, the optical systems may include an anamorphic lens that is oriented to correct for astigmatism caused by surface errors of the reflective surface of the prism.

This application is a continuation of U.S. patent application Ser. No.17/329,009, filed May 24, 2021, which claims benefit of priority to U.S.Provisional Application Ser. No. 63/030,224, entitled “Folded OpticalSystems,” filed May 26, 2020, and which are incorporated herein byreference in their entirety.

BACKGROUND Technical Field

This disclosure relates generally to camera systems, and morespecifically to folded optical systems.

Description of the Related Art

The advent of small, mobile multipurpose devices such as smartphones andtablet or pad devices has resulted in a need for high-resolution, smallform factor cameras that are lightweight, compact, and capable ofcapturing high resolution, high quality images at low F-numbers forintegration in the devices. However, due to limitations of conventionalcamera technology, conventional small cameras used in such devices tendto capture images at lower resolutions and/or with lower image qualitythan can be achieved with larger, higher quality cameras. Achievinghigher resolution with small package size cameras generally requires useof an image sensor with small pixel size and a good, compact imaginglens system. Advances in technology have achieved reduction of the pixelsize in image sensors. However, as image sensors become more compact andpowerful, demand for compact imaging lens systems with improved imagingquality performance has increased. In addition, there are increasingexpectations for small form factor cameras to be equipped with higherpixel count and/or larger pixel size image sensors (one or both of whichmay require larger image sensors) while still maintaining a moduleheight that is compact enough to fit into portable electronic devices.Thus, a challenge from an optical system design point of view is toprovide an optical system that is capable of capturing high brightness,high resolution images under the physical constraints imposed by smallform factor cameras.

SUMMARY OF EMBODIMENTS

Embodiments of single fold optical systems that include a single prismwith optical power (referred to as a power prism) and a lens stackincluding two or more refractive lens elements are described. The powerprism may be referred to as a first lens group, and the lens stack maybe referred to as a second lens group. The single folded optical systemsmay provide reduced Z-axis height and reduced X-axis length whencompared to conventional double folded optical systems with similaroptical characteristics. Embodiments of the single fold optical systemsmay, for example, be used in small form factor cameras in mobilemultipurpose devices such as smartphones and tablet or pad devices.

In some embodiments, the power prism is formed of an optical plasticmaterial, and the object side surface of the prism is a curved sphericalor aspherical surface to provide refractive power. In some embodiments,the power prism is an optical glass triangular prism with a refractivelens formed of an optical plastic attached to the object side of theprism to provide refractive power. In some embodiments, the power prismis an optical glass triangular prism with a refractive lens formed of anoptical glass attached to the object side of the prism.

In addition, embodiments of folded optical systems that include at leastone anamorphic lens that is oriented to correct for aberrationsincluding astigmatism caused by surface errors of the reflective surfaceof the prism(s) in the folded optical systems are described. Ananamorphic lens as described herein may, for example, be used inembodiments of the single fold optical systems that include a singlepower prism as described herein. However, anamorphic lenses as describedherein may also be used in other single fold optical systems or doublefold optical systems to correct for aberrations including astigmatismcaused by surface errors of the reflective surface(s) of the prism(s) inthe folded optical systems. Anamorphic lenses as described herein may beused to correct for aberrations caused by the flat reflective surfacesof power prisms or triangular prisms or by the curved reflectivesurfaces of prisms such as freeform prisms.

A manufacturing process for folded optical systems that includeanamorphic lenses to correct for aberrations including astigmatismcaused by surface errors of the reflective surface(s) of the prism(s) isalso described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example single fold optical system that includes apower prism composed of an optical plastic, according to someembodiments.

FIG. 2 illustrates an example single fold optical system that includes aglass prism and a plastic lens on the object side of the prism,according to some embodiments.

FIG. 3 illustrates an example single fold optical system that includes aglass prism and a glass lens on the object side of the prism, accordingto some embodiments.

FIG. 4 illustrates example optical characteristics and performancemetrics of an example optical system as illustrated in FIG. 1 .

FIGS. 5A and 5B compare a double fold optical system to a single foldoptical system, according to some embodiments.

FIG. 6A illustrates another example single fold optical system thatincludes a power prism composed of an optical plastic, according to someembodiments.

FIG. 6B illustrates optical characteristics and performance metrics ofthe example optical system illustrated in FIG. 6A.

FIG. 7A illustrates another example single fold optical system thatincludes a glass prism and a plastic lens on the object side of theprism, according to some embodiments.

FIG. 7B illustrates optical characteristics and performance metrics ofthe example optical system illustrated in FIG. 7A.

FIG. 8A illustrates another example single fold optical system thatincludes a glass prism and a glass lens on the object side of the prism,according to some embodiments.

FIG. 8B illustrates optical characteristics and performance metrics ofthe example optical system illustrated in FIG. 8A.

FIG. 9A illustrates another example single fold optical system thatincludes a power prism, according to some embodiments.

FIG. 9B illustrates optical characteristics and performance metrics ofthe example optical system illustrated in FIG. 9A.

FIG. 10 is a flowchart of a method for capturing images usingembodiments of a single fold optical system as illustrated in FIGS. 1through 9 , according to some embodiments.

FIG. 11 shows surfaces of an example single fold optical system asreferred to in the Tables.

FIGS. 12A through 12D illustrate using an anamorphic lens in a lensstack to correct aberrations including astigmatism caused by surfaceerrors of the reflective surface of a prism in a folded optical system,according to some embodiments.

FIG. 13 illustrates using an anamorphic lens in a lens stack to correctaberrations including astigmatism caused by surface errors of thereflective surface of a prism in a double fold optical system, accordingto some embodiments.

FIG. 14 illustrates using an anamorphic lens to correct aberrationsincluding astigmatism caused by a freeform prism, according to someembodiments.

FIG. 15 is a high-level flowchart of a method of manufacturing a foldedoptical system that includes an anamorphic lens oriented to correct foraberrations including astigmatism caused by surface errors of thereflective surface of a prism in a folded optical system, according tosome embodiments.

FIG. 16 illustrates an example computer system.

This specification includes references to “one embodiment” or “anembodiment.” The appearances of the phrases “in one embodiment” or “inan embodiment” do not necessarily refer to the same embodiment.Particular features, structures, or characteristics may be combined inany suitable manner consistent with this disclosure.

“Comprising.” This term is open-ended. As used in the appended claims,this term does not foreclose additional structure or steps. Consider aclaim that recites: “An apparatus comprising one or more processor units. . . ”. Such a claim does not foreclose the apparatus from includingadditional components (e.g., a network interface unit, graphicscircuitry, etc.).

“Configured To.” Various units, circuits, or other components may bedescribed or claimed as “configured to” perform a task or tasks. In suchcontexts, “configured to” is used to connote structure by indicatingthat the units/circuits/components include structure (e.g., circuitry)that performs those task or tasks during operation. As such, theunit/circuit/component can be said to be configured to perform the taskeven when the specified unit/circuit/component is not currentlyoperational (e.g., is not on). The units/circuits/components used withthe “configured to” language include hardware—for example, circuits,memory storing program instructions executable to implement theoperation, etc. Reciting that a unit/circuit/component is “configuredto” perform one or more tasks is expressly intended not to invoke 35U.S.C. § 112(f), for that unit/circuit/component. Additionally,“configured to” can include generic structure (e.g., generic circuitry)that is manipulated by software and/or firmware (e.g., an FPGA or ageneral-purpose processor executing software) to operate in manner thatis capable of performing the task(s) at issue. “Configure to” may alsoinclude adapting a manufacturing process (e.g., a semiconductorfabrication facility) to fabricate devices (e.g., integrated circuits)that are adapted to implement or perform one or more tasks.

“First,” “Second,” etc. As used herein, these terms are used as labelsfor nouns that they precede, and do not imply any type of ordering(e.g., spatial, temporal, logical, etc.). For example, a buffer circuitmay be described herein as performing write operations for “first” and“second” values. The terms “first” and “second” do not necessarily implythat the first value must be written before the second value.

“Based On.” As used herein, this term is used to describe one or morefactors that affect a determination. This term does not forecloseadditional factors that may affect a determination. That is, adetermination may be solely based on those factors or based, at least inpart, on those factors. Consider the phrase “determine A based on B.”While in this case, B is a factor that affects the determination of A,such a phrase does not foreclose the determination of A from also beingbased on C. In other instances, A may be determined based solely on B.

DETAILED DESCRIPTION

Embodiments of a single fold optical system are described that may, forexample, be used in small form factor cameras in mobile multipurposedevices such as smartphones and tablet or pad devices. Conventionaldouble folded optical systems may include two prisms and a lens stackincluding two or more refractive lens elements. A first prism redirectslight from a first optical axis to the lens stack on a second opticalaxis. A second prism located at the image side of the lens stack foldsthe optical axis on to a third axis where an image is formed at an imageplane at or near the surface of a photosensor.

Embodiments of single fold optical systems that include a single prismwith optical power (referred to as a power prism) and a lens stackincluding two or more refractive lens elements as described herein mayprovide an optical system with long focal length and reduced thickness(Z-height) and X-length when compared to a double folded optical systemwith similar optical characteristics. In general, the Z-height of doublefolded optics is defined by the prism size and mechanical back focus.Embodiments of the single fold optical system may provide a longmechanical back focus without increasing the Z-height of the opticalsystem. Providing power on the prism may reduce the optical total lengthand reduce the X-length of the optical system.

In some embodiments, the power prism in the single fold optical systemis formed of an optical plastic material, and the object side surface ofthe prism is a curved spherical or aspherical surface to providerefractive power. In some embodiments, the power prism is an opticalglass triangular prism with a refractive lens formed of an opticalplastic attached to the object side of the prism to provide refractivepower. A first surface of the lens may be an aspherical or sphericalsurface. In some embodiments, the power prism is an optical glasstriangular prism with a refractive lens formed of an optical glassattached to the object side of the prism. A first surface of the lensmay be an aspherical or spherical surface. Note that the power prism hasmore than three surfaces; however, only three of the surfaces of thepower prism are discussed; an object side surface with curvature thatprovides refractive power; a reflective surface that acts to fold theoptical axis; and an image side surface through which light from thereflective surface exits the power prism towards the lens stack orsecond lens group.

In addition, embodiments of folded optical systems that include at leastone anamorphic lens that is oriented to correct for aberrationsincluding astigmatism caused by surface errors of the reflective surfaceof the prism(s) in the folded optical systems are described. Ananamorphic lens as described herein may, for example, be used inembodiments of the single fold optical systems that include a singlepower prism as described herein. However, anamorphic lenses as describedherein may also be used in other single fold optical systems or doublefold optical systems to correct for aberrations including astigmatismcaused by surface errors of the reflective surface(s) of the prism(s) inthe folded optical systems. Anamorphic lenses as described herein may beused to correct for aberrations caused by the flat reflective surfacesof power prisms or triangular prisms or by the curved reflectivesurfaces of prisms such as freeform prisms. Freeform optics involveoptical designs with at least one surface which has no translational orrotational symmetry about axes normal to the mean plane of the surface.A freeform prism is thus a prism that has at least one surface which hasno translational or rotational symmetry about axes normal to the meanplane of the surface.

A manufacturing process for folded optical systems that includeanamorphic lenses to correct for aberrations including astigmatismcaused by surface errors of the reflective surface(s) of the prism(s) isalso described.

FIGS. 1 through 3 illustrate side cutaway views of example embodimentsof single fold optical systems as described herein. As shown in FIGS. 1through 3 , the single fold optical system may include:

a first lens group that includes a power prism formed of an opticalplastic material with an aspherical object side surface as shown in FIG.1 , or that includes a triangular glass prism with a positive lensformed of an optical plastic or glass material having an asphericalobject side surface and a flat or plano image side surface attached tothe object side surface of the prism as shown in FIGS. 2 and 3 ; and asecond lens group that includes two or more refractive lens elements(four, in these embodiments). The refractive lenses in the second lensgroup may be formed of optical plastic or glass materials. In someembodiments, all of the refractive lenses in the second lens group maybe formed of the same material. In some embodiments, at least two of therefractive lenses in the second lens group may be formed of differentmaterials.

In some embodiments of the single fold optical system, the first (objectside) surface of the first lens group is aspherical, and the anglebetween the principal ray that passes through the first surface of thefirst lens group and the principal ray at an image plane formed on theimage side of the second lens group may be, but is not necessarily, lessthan 90 degrees.

Embodiments of the single fold optical system may satisfy the followingconditional expression:

0.6<B/A<2.3,

where A is the power of the total optical system, and B is the power ofthe first lens group. If B/A is larger than the range expressed in theconditional expression, the amount of sag may be too large tomanufacture. On the other hand, if B/A is smaller than the rangeexpressed in the conditional expression, the X-length of optical systemcannot be reduced effectively.

Embodiments of the single fold optical system may satisfy the followingconditional expression:

−0.2<CD<0.1,

where C is the power of the second lens group, and D is the length ofthe second lens group. CD applies to the sensitivity of the second lensgroup. If CD is not within the range expressed in the conditionalexpression, the tolerance of second lens group may not be good and/orthe size (length) of the second lens group may be enlarged.

In some embodiments, the prism in the first lens group is composed of anoptical material with an Abbe number V_(d) that satisfies the followingcondition:

V _(d)>50.

Embodiments of the single fold optical system as described herein mayhave a Z-height of <7.3 mm, and an X-length of <18 mm.

In some embodiments, one or more of the optical elements in the opticalsystem may be formed using an injection molding process. However, insome embodiments, other methods may be used to form one or more of theseelements (e.g., 3D printing, extrusion, blow molding, casting,rotomolding, die cast, overmolding, compression molding, computernumerical control (CNC) machining, thermoforming, etc.).

FIG. 1 illustrates a single fold optical system that includes a powerprism composed of an optical plastic, according to some embodiments.Optical system 100 may include a power prism 110 (also referred to as afirst lens group) and a lens stack 120 (also referred to as a secondlens group) that includes two or more refractive lenses. In thisexample, lens stack 120 includes four refractive lenses: lens 121, lens122, lens 123, and lens 124. Note, however, that some embodiments mayinclude more or fewer lenses in lens stack 120. An aperture stop 102 maybe located at or near the object side of the power prism 110.

The power prism 110 may be formed of an optical plastic material. Insome embodiments, the object side surface 112 of the prism 110 is acurved aspherical surface that provides positive refractive power forthe prism 110. A second surface 114 of the prism 110 is a flat or planosurface that reflects, via total internal reflection (TIR) or via amirror coating, light received from an object field through the objectside surface 112 of the prism 110 to thus fold the optical axis of theoptical system 100. The light reflected by the second surface 114 exitsthe prism 110 through a third flat or plano surface 116 to a first lens121 in the lens stack 120. The lenses in the lens stack 120 then refractthe light to form an image at an image plane.

FIG. 1 shows an example lens stack 120 that includes four refractivelenses: lens 121 with positive refractive power, lens 122 with negativerefractive power, lens 123 with negative refractive power, and lens 124with positive refractive power. Note, however, that some embodiments mayinclude more or fewer lenses in lens stack 120. In addition, thematerial, shape, power, power order, position, and distance between thelenses is given by way of example, and is not intended to be limiting.

The single fold optical system 100 of FIG. 1 may form an image at animage plane at or near a surface of an image sensor 140 located on theimage side of the lens stack 120. In some embodiments, an infrared (IR)filter 130 may be located between lens stack 120 and the image sensor140. The optical system 100, sensor 140, and filter 130 (if present) maybe components of a camera that may, for example, be used as a small formfactor camera in mobile multipurpose devices such as smartphones andtablet or pad devices.

FIG. 2 illustrates an example single fold optical system that includes aglass prism and a plastic lens on the object side of the prism,according to some embodiments. Optical system 200 may include a lens 204formed of an optical plastic material and a prism 210 formed of anoptical glass material (collectively referred to as a first lens group)and a lens stack 220 (also referred to as a second lens group) thatincludes two or more refractive lenses. In this example, lens stack 220includes four refractive lenses: lens 221, lens 222, lens 223, and lens224. Note, however, that some embodiments may include more or fewerlenses in lens stack 220. An aperture stop 202 may be located at or nearthe object side of the lens 204.

The prism 210 may be formed of an optical glass material. The objectside surface 212 of the prism 210 is a flat or plano surface. A plasticlens 204 with positive refractive power may be attached to the objectside surface 212 of the prism 210, for example with an adhesivematerial. The object side surface of lens 204 may be a spherical oraspherical convex surface; the image side surface of lens 204 is a flator plano surface. A second surface 214 of the prism 210 is a flat orplano surface that reflects, via total internal reflection (TIR) or viaa mirror coating, light received from an object field through the objectside surface 212 of the prism 210 to thus fold the optical axis of theoptical system 200. The light reflected by the second surface 214 exitsthe prism 210 through a third flat or plano surface 216 to a first lens221 in the lens stack 220. The lenses in the lens stack 220 then refractthe light to form an image at an image plane.

FIG. 2 shows an example lens stack 220 that includes four refractivelenses: lens 221 with positive refractive power, lens 222 with negativerefractive power, lens 223 with negative refractive power, and lens 224with positive refractive power. Note, however, that some embodiments mayinclude more or fewer lenses in lens stack 220. In addition, thematerial, shape, power, power order, position, and distance between thelenses is given by way of example, and is not intended to be limiting.

The single fold optical system 200 of FIG. 2 may form an image at animage plane at or near a surface of an image sensor 240 located on theimage side of the lens stack 220. In some embodiments, an infrared (IR)filter 230 may be located between lens stack 220 and the image sensor240. The optical system 200, sensor 240, and filter 230 (if present) maybe components of a camera that may, for example, be used as a small formfactor camera in mobile multipurpose devices such as smartphones andtablet or pad devices.

FIG. 3 illustrates an example single fold optical system that includes aglass prism and a glass lens on the object side of the prism, accordingto some embodiments. Optical system 300 may include a lens 304 formed ofan optical glass material and a prism 310 formed of an optical glassmaterial (collectively referred to as a first lens group) and a lensstack 320 (also referred to as a second lens group) that includes two ormore refractive lenses. In this example, lens stack 320 includes fourrefractive lenses: lens 321, lens 322, lens 323, and lens 324. Note,however, that some embodiments may include more or fewer lenses in lensstack 320. An aperture stop 302 may be located at or near the objectside of the lens 304.

The prism 310 may be formed of an optical glass material. The objectside surface 312 of the prism 310 is a flat or plano surface. A glasslens 304 with positive refractive power may be attached to the objectside surface 312 of the prism 310, for example with an adhesivematerial. The object side surface of lens 304 may be a spherical oraspherical convex surface; the image side surface of lens 304 is a flator plano surface. A second surface 314 of the prism 310 is a flat orplano surface that reflects, via total internal reflection (TIR) or viaa mirror coating, light received from an object field through the objectside surface 312 of the prism 310 to thus fold the optical axis of theoptical system 300. The light reflected by the second surface 314 exitsthe prism 310 through a third flat or plano surface 316 to a first lens321 in the lens stack 320. The lenses in the lens stack 320 then refractthe light to form an image at an image plane.

FIG. 3 shows an example lens stack 320 that includes four refractivelenses: lens 321 with positive refractive power, lens 322 with negativerefractive power, lens 223 with negative refractive power, and lens 324with positive refractive power. Note, however, that some embodiments mayinclude more or fewer lenses in lens stack 320. In addition, thematerial, shape, power, power order, position, and distance between thelenses is given by way of example, and is not intended to be limiting.

The single fold optical system 300 of FIG. 3 may form an image at animage plane at or near a surface of an image sensor 340 located on theimage side of the lens stack 320. In some embodiments, an infrared (IR)filter 330 may be located between lens stack 320 and the image sensor340. The optical system 300, sensor 340, and filter 330 (if present) maybe components of a camera that may, for example, be used as a small formfactor camera in mobile multipurpose devices such as smartphones andtablet or pad devices.

FIG. 4 illustrates example optical characteristics and performancemetrics of an example optical system as illustrated in FIG. 1 . Theexample optical system may have an X length of 15.5 millimeters (mm),and a Z height of 6.8 mm. Distortion of the optical systems may be<+/−0.25%. The graphs show the modulation transfer function (MTF) of thesingle fold optical systems at infinity (inf) and at macro.

FIGS. 5A and 5B compare a double fold optical system to a single foldoptical system, according to some embodiments. FIG. 5A shows an exampleconventional double folded optical system 500A that includes, in orderfrom an object side to an image side, a first prism that folds theoptical axis a first time, a lens stack, and a second prism or mirrorthat folds the optical axis a second time; an image is formed at animage plane at or near a sensor. Z-height of the optical system 500A maybe about 7.1 mm, while X-length may be about 22.3 mm. FIG. 5B shows anexample embodiment of a single fold optical system 500B as describedherein that includes, in order from an object side to an image side, afirst lens group (power prism) that folds the optical axis, and a secondlens group (lens stack) that refracts light received from the first lensgroup to form an image at an image plane at or near a sensor. Z-heightof the optical system 500B may be about 6.8 mm, while X-length may beabout 15.5 mm.

As shown in FIGS. 5A and 5B, embodiments of the single fold opticalsystem as described herein may provide an optical system with long focallength and reduced thickness (Z-height) and X-length when compared to aconventional double folded optical system with similar opticalcharacteristics. In general, the Z-height of double folded optics isdefined by the prism size and mechanical back focus. Embodiments of thesingle fold optical system may provide a long mechanical back focuswithout increasing, or even decreasing, the Z-height of the opticalsystem. Providing power on the prism may reduce the optical total lengthand reduce the X-length of the optical system.

FIGS. 6A-6B, 7A-7B, 8A-8B, and 9 illustrate side cutaway views ofadditional example embodiments of single fold optical systems asdescribed herein.

FIG. 6A illustrates another example single fold optical system thatincludes a power prism composed of an optical plastic, according to someembodiments. Optical system 600 may include a power prism 610 (alsoreferred to as a first lens group) and a lens stack 620 (also referredto as a second lens group) that includes four refractive lenses: lens621, lens 622, lens 623, and lens 624. Note, however, that someembodiments may include more or fewer lenses in lens stack 620. Anaperture stop 602 may be located at or near the object side of the powerprism 610.

The power prism 610 may be formed of an optical plastic material. Insome embodiments, the object side surface 612 of the prism 610 is acurved aspherical surface that provides positive refractive power forthe prism 610. A second surface 614 of the prism 610 is a flat or planosurface that reflects, via total internal reflection (TIR) or via amirror coating, light received from an object field through the objectside surface 612 of the power prism 610 to thus fold the optical axis ofthe optical system 600. The light reflected by the second surface 614exits the prism 610 through a third flat or plano surface 616 to a firstlens 621 in the lens stack 620. The lenses in the lens stack 620 thenrefract the light to form an image at an image plane.

FIG. 6A shows an example lens stack 620 that includes four refractivelenses: lens 621 with positive refractive power, lens 622 with negativerefractive power, lens 623 with negative refractive power, and lens 624with positive refractive power. Note, however, that some embodiments mayinclude more or fewer lenses in lens stack 620. In some embodiments, atleast one surface of at least one of the lenses in the second lens groupmay be an aspherical surface. The refractive lenses in the second lensgroup may be formed of optical plastic or glass materials. In addition,the material, shape, power, power order, position, and distance betweenthe lenses is given by way of example, and is not intended to belimiting.

The single fold optical system 600 of FIG. 6A may form an image at animage plane at or near a surface of an image sensor 640 located on theimage side of the lens stack 620. In some embodiments, an infrared (IR)filter 630 may be located between lens stack 620 and the image sensor640. The optical system 600, sensor 640, and filter 630 (if present) maybe components of a camera that may, for example, be used as a small formfactor camera in mobile multipurpose devices such as smartphones andtablet or pad devices.

FIG. 6B illustrates optical characteristics and performance metrics ofthe example optical system 600 illustrated in FIG. 6A. The exampleoptical system 600 may have an X length of 17.2 millimeters (mm), and aZ height of 6.8 mm. Distortion of the optical systems may be <+/−0.25%.The graphs show the modulation transfer function (MTF) of the singlefold optical systems at infinity (inf) and at macro.

FIG. 7A illustrates another example single fold optical system thatincludes a glass prism and a plastic lens on the object side of theprism, according to some embodiments. Optical system 700 may include alens 704 formed of an optical plastic material and a prism 710 formed ofan optical glass material (collectively referred to as a first lensgroup) and a lens stack 720 (also referred to as a second lens group)that includes four refractive lenses: lens 721, lens 722, lens 723, andlens 724. Note, however, that some embodiments may include more or fewerlenses in lens stack 720. An aperture stop 702 may be located at or nearthe object side of the lens 704.

The prism 710 may be formed of an optical glass material. The objectside surface 712 of the prism 710 is a flat or plano surface. A plasticlens 704 with positive refractive power may be attached to the objectside surface 712 of the prism 710, for example with an adhesivematerial. The object side surface of lens 704 may be a spherical oraspherical convex surface; the image side surface of lens 704 is a flator plano surface. A second surface 714 of the prism 710 is a flat orplano surface that reflects, via total internal reflection (TIR) or viaa mirror coating, light received from an object field through the objectside surface 712 of the prism 710 to thus fold the optical axis of theoptical system 700. The light reflected by the second surface 714 exitsthe prism 710 through a third flat or plano surface 716 to a first lens721 in the lens stack 720. The lenses in the lens stack 720 then refractthe light to form an image at an image plane.

FIG. 7A shows an example lens stack 720 that includes four refractivelenses: lens 721 with positive refractive power, lens 722 with negativerefractive power, lens 723 with negative refractive power, and lens 724with positive refractive power. Note, however, that some embodiments mayinclude more or fewer lenses in lens stack 720. In some embodiments, atleast one surface of at least one of the lenses in the second lens groupmay be an aspherical surface. The refractive lenses in the second lensgroup may be formed of optical plastic or glass materials. In addition,the material, shape, power, power order, position, and distance betweenthe lenses is given by way of example, and is not intended to belimiting.

The single fold optical system 700 of FIG. 7A may form an image at animage plane at or near a surface of an image sensor 740 located on theimage side of the lens stack 720. In some embodiments, an infrared (IR)filter 730 may be located between lens stack 720 and the image sensor740. The optical system 700, sensor 740, and filter 730 (if present) maybe components of a camera that may, for example, be used as a small formfactor camera in mobile multipurpose devices such as smartphones andtablet or pad devices.

FIG. 7B illustrates optical characteristics and performance metrics ofthe example optical system 700 illustrated in FIG. 7A. The exampleoptical system 700 may have an X length of 17.2 millimeters (mm), and aZ height of 6.5 mm. Distortion of the optical systems may be <+/−0.25%.The graphs show the modulation transfer function (MTF) of the singlefold optical systems at infinity (inf) and at macro.

FIG. 8A illustrates another example single fold optical system thatincludes a glass prism and a glass lens on the object side of the prism,according to some embodiments. Optical system 800 may include a lens 804formed of an optical glass material and a prism 810 formed of an opticalglass material (collectively referred to as a first lens group) and alens stack 820 (also referred to as a second lens group) that includesfour refractive lenses: lens 821, lens 822, lens 823, and lens 824.Note, however, that some embodiments may include more or fewer lenses inlens stack 820. An aperture stop 802 may be located at or near theobject side of the lens 804.

The prism 810 may be formed of an optical glass material. The objectside surface 812 of the prism 810 is a flat or plano surface. A glasslens 804 with positive refractive power may be attached to the objectside surface 812 of the prism 8710, for example with an adhesivematerial. The object side surface of lens 804 may be a spherical oraspherical convex surface; the image side surface of lens 804 is a flator plano surface. A second surface 814 of the prism 810 is a flat orplano surface that reflects, via total internal reflection (TIR) or viaa mirror coating, light received from an object field through the objectside surface 812 of the prism 810 to thus fold the optical axis of theoptical system 800. The light reflected by the second surface 814 exitsthe prism 810 through a third flat or plano surface 816 to a first lens821 in the lens stack 820. The lenses in the lens stack 820 then refractthe light to form an image at an image plane.

FIG. 8A shows an example lens stack 820 that includes four refractivelenses: lens 821 with positive refractive power, lens 822 with negativerefractive power, lens 823 with negative refractive power, and lens 824with positive refractive power. Note, however, that some embodiments mayinclude more or fewer lenses in lens stack 820. In some embodiments, atleast one surface of at least one of the lenses in the second lens groupmay be an aspherical surface. The refractive lenses in the second lensgroup may be formed of optical plastic or glass materials. In addition,the material, shape, power, power order, position, and distance betweenthe lenses is given by way of example, and is not intended to belimiting.

The single fold optical system 800 of FIG. 8A may form an image at animage plane at or near a surface of an image sensor 840 located on theimage side of the lens stack 820. In some embodiments, an infrared (IR)filter 830 may be located between lens stack 820 and the image sensor840. The optical system 800, sensor 840, and filter 830 (if present) maybe components of a camera that may, for example, be used as a small formfactor camera in mobile multipurpose devices such as smartphones andtablet or pad devices.

FIG. 8B illustrates optical characteristics and performance metrics ofthe example optical system 800 illustrated in FIG. 8A. The exampleoptical system 800 may have an X length of 17.2 millimeters (mm), and aZ height of 7.1 mm. Distortion of the optical systems may be <+/−0.25%.The graphs show the modulation transfer function (MTF) of the singlefold optical systems at infinity (inf) and at macro.

FIG. 9A illustrates another example single fold optical system thatincludes a power prism, according to some embodiments. Optical system900 may include a power prism 910 (also referred to as a first lensgroup) and a lens stack 920 (also referred to as a second lens group)that includes four refractive lenses: lens 921, lens 922, lens 923, andlens 924. Note, however, that some embodiments may include more or fewerlenses in lens stack 920. An aperture stop 902 may be located at or nearthe object side of the power prism 910.

The power prism 910 may be formed of an optical plastic material. Insome embodiments, the object side surface 912 of the prism 910 is acurved aspherical surface that provides positive refractive power forthe prism 910. A second surface 914 of the prism 910 is a flat or planosurface that reflects, via total internal reflection (TIR) or via amirror coating, light received from an object field through the objectside surface 912 of the power prism 910 to thus fold the optical axis ofthe optical system 900. The light reflected by the second surface 914exits the prism 910 through a third flat or plano surface 916 to a firstlens 921 in the lens stack 920. The lenses in the lens stack 920 thenrefract the light to form an image at an image plane.

FIG. 9A shows an example lens stack 920 that includes four refractivelenses: lens 921 with positive refractive power, lens 922 with negativerefractive power, lens 923 with negative refractive power, and lens 924with positive refractive power. Note, however, that some embodiments mayinclude more or fewer lenses in lens stack 920. In some embodiments, atleast one surface of at least one of the lenses in the second lens groupmay be an aspherical surface. The refractive lenses in the second lensgroup may be formed of optical plastic or glass materials. In addition,the material, shape, power, power order, position, and distance betweenthe lenses is given by way of example, and is not intended to belimiting.

The single fold optical system 900 of FIG. 9A may form an image at animage plane at or near a surface of an image sensor 940 located on theimage side of the lens stack 920. In some embodiments, an infrared (IR)filter 930 may be located between lens stack 920 and the image sensor940. The optical system 900, sensor 940, and filter 930 (if present) maybe components of a camera that may, for example, be used as a small formfactor camera in mobile multipurpose devices such as smartphones andtablet or pad devices.

FIG. 9B illustrates optical characteristics and performance metrics ofthe example optical system 900 illustrated in FIG. 9A. The exampleoptical system 900 may have an X length of 17.6 millimeters (mm), and aZ height of 7.2 mm. Distortion of the optical systems may be <+/−0.25%.The graphs show the modulation transfer function (MTF) of the singlefold optical systems at infinity (inf) and at macro.

FIG. 10 is a flowchart of a method for capturing images usingembodiments of a single fold optical system as illustrated in FIGS. 1through 9 , according to some embodiments. As indicated at 1000, lightfrom an object field is received through an aperture at a first surfaceof a power prism. As indicated at 1010, the first surface of the powerprism refracts the light to a second (reflective) surface of the powerprism. As indicated at 1020, the second surface of the power prismreflects the light to a third surface of the power prism. As indicatedat 1030, the third surface of the prism transmits the light to a lensstack. As indicated at 1040, the refractive lenses in the lens stackrefract the light to form an image at an image plane at or near asurface of an image sensor. In some embodiments, an infrared filter maybe positioned between the lens stack and the image sensor.

The following tables provide optical and physical characteristics of theexample single fold lens systems described herein. FIG. 11 showssurfaces of an example single fold optical system as referred to in theTables. Each surface location is determined by the global coordinatebased on Prism S1.

An aspherical surface may be defined as:

$z = {\frac{\frac{h^{2}}{r}}{1 + \sqrt{1 - \frac{\left( {1 + k} \right)h^{2}}{r^{2}}}} + {Ah}^{2} + {Bh^{2}} + {Ch^{2}} + \ldots}$

where

h=√{square root over (x ² +y ²)}

and where radius of curvature r is:

4th order (A); 6th order (B); 8th order (C); 10th order (D); 12th order(E); and 14th order (F).

Table 1 provides ranges of optical and physical characteristics of theexample embodiments shown in FIGS. 1, 6A, 7A, 8A, and 9A.

TABLE 1 Character- istic Range FIG. 1 FIG. 6A FIG. 7A FIG. 8A FIG. 9AB/A 0.6-2.3 1.24 0.81 0.81 0.81 2.10 CD −0.2-0.1  −0.128 0.047 0.0470.046 −0.106 Vd1 >50 55.97 55.73 55.73 55.73 55.73 Z-height <7.3 6.8 6.86.5 7.1 7.2 X-length <18 15.5 17.2 17.2 17.2 17.6

Tables 2A through 2F provide optical and physical characteristics forthe example single fold optical system as illustrated in FIG. 1 .

Table 2A shows all surface positions based on the Prism S1 globalcoordinate for the example single fold optical system as illustrated inFIG. 1 :

TABLE 2A x z angle (α) aperture 0 0.3 0 Prism S1 0.000 0.000 0 Prism S20.000 3.800 45 Prism S3 −3.400 3.800 90 L1 S1 −3.500 3.800 90 L1S2−4.320 3.800 90 L2S1 −4.712 3.800 90 L2S2 −5.102 3.800 90 L3S1 −8.0703.800 90 L3S4 −8.737 3.800 90 L4S1 −9.070 3.800 90 L4S2 −10.225 3.800 90IRcut S1 −11.890 3.800 90 IRcut S2 −12.100 3.800 90 image plane (INF)−12.200 3.800 90

Tables 2B through 2D show aspherical values for the surfaces of theoptical components for the example single fold optical system asillustrated in FIG. 1 :

TABLE 2B Prism S1 L1S1 L1S2 Radius of curvature 6.7203 −5.2935 14.26034th order −4.26730E−04 −2.88851E−03 −1.48664E−03 6th order −1.29339E−05−3.95461E−04  9.32386E−04 8th order −7.66845E−07  9.90583E−05−6.91378E−05 10th order  6.66654E−08 −1.12263E−05 −3.43883E−06 12thorder −5.16169E−09  2.23130E−06  3.08245E−06 14th order  4.49321E−07−2.03270E−07

TABLE 2C L2S1 L2S2 L3S1 Radius of curvature −16.1429 −2.7451 3.7738 4thorder  1.41735E−02  1.19869E−02  1.31664E−02 6th order −6.22662E−04−2.57413E−03 −2.21852E−03 8th order −1.17735E−04  4.39224E−04 6.21870E−04 10th order −3.12763E−05 −5.79999E−04 −1.72582E−04 12thorder −4.96180E−07  2.09980E−04 14th order −4.53847E−07 −4.24766E−05

TABLE 2D L3S2 L4S1 L4S2 Radius of curvature −10.1283 −15.1458 5.1079 4thorder  1.57161E−02  3.58922E−03  2.66831E−03 6th order −2.19959E−03−5.01016E−04 −8.20924E−04 8th order  3.69265E−04 −8.42268E−05 9.61069E−05 10th order −4.01054E−05  3.08659E−05 −2.99277E−05 12thorder −4.44401E−06  4.12343E−06 14th order  2.08392E−07 −2.22745E−07

Table 2E shows material characteristics of the optical components forthe example single fold optical system as illustrated in FIG. 1 . Ndrefers to refractive index, and Vd refers to Abbe number of thematerial. L1-L4 refer to the four lenses in the second lens group fromthe object side to the image side of the optical system:

TABLE 2E Prism L1 L2 L3 L4 Nd 1.544 1.544 1.671 1.544 1.671 Vd 55.9755.97 19.23 55.97 19.23

Table 2F shows optical specifications for the example single foldoptical system as illustrated in FIG. 1 . EFL is effective focal length,and Fno is the F-number of the optical system:

TABLE 2F EFL 15.3 Fno 3.0 semi-sensor diagonal 2.52 Macro distance 80 cm

Tables 3A through 3F provide optical and physical characteristics forthe example single fold optical system as illustrated in FIG. 6A.

Table 3A shows all surface positions based on the Prism S1 globalcoordinate for the example single fold optical system as illustrated inFIG. 6A:

TABLE 3A x z angle (α) aperture 0 0.28 0 Prism S1 0.000 0.000 0 Prism S20.000 3.450 45 Prism S3 −3.100 3.450 90 L1 S1 −3.600 3.450 90 L1S2−4.645 3.450 90 L2S1 −4.898 3.450 90 L2S2 −5.288 3.450 90 L3S1 −8.9743.450 90 L3S4 −9.634 3.450 90 L4S1 −10.375 3.450 90 L4S2 −11.475 3.45090 IRcut S1 −13.359 3.450 90 IRcut S2 −13.569 3.450 90 image plane (INF)−13.669 3.450 90

Tables 3B through 3D show aspherical values for the surfaces of theoptical components for the example single fold optical system asillustrated in FIG. 6A:

TABLE 3B Prism S1 L1S1 L1S2 Radius of curvature 10.1475 −4.5962 24.13704th order −5.10336E−04 −4.96952E−03 −6.96106E−03 6th order  1.31446E−07 3.25426E−04  2.34753E−03 8th order −8.33779E−07 −2.59701E−05−5.13966E−04 10th order  1.26361E−07  3.54569E−05  1.47389E−04 12thorder −5.84423E−09 −7.43090E−06 −1.18246E−05 14th order  1.91989E−06 1.99593E−07

TABLE 3C L2S1 L2S2 L3S1 Radius of curvature −5.8392 −2.7004 7.9220 4thorder  2.08846E−02  2.80123E−02  4.36643E−02 6th order −6.99973E−03−1.15153E−02 −8.56777E−03 8th order  9.61573E−04  2.21425E−03 4.95687E−04 10th order −3.49028E−05 −6.01848E−04 −4.46371E−05 12thorder −8.47955E−07  1.40503E−04 14th order −2.38157E−06 −2.85205E−05

TABLE 3D L3S2 L4S1 L4S2 Radius of curvature −5.3114 −81.4716 6.5864 4thorder  3.90863E−02 −1.94553E−03  8.73233E−04 6th order −8.82724E−03 1.24447E−03 −2.40538E−04 8th order  1.21063E−03 −3.53784E−04 4.64840E−05 10th order −9.15778E−05  8.00536E−05 −2.44547E−06 12thorder −7.42994E−06  1.63492E−06 14th order  4.81112E−07 −3.05210E−08

Table 3E shows material characteristics of the optical components forthe example single fold optical system as illustrated in FIG. 6A. Ndrefers to refractive index, and Vd refers to Abbe number of thematerial. L1-L4 refer to the four lenses in the second lens group fromthe object side to the image side of the optical system:

TABLE 3E Prism L1 L2 L3 L4 Nd 1.535 1.544 1.671 1.544 1.671 Vd 55.7355.97 19.23 55.97 19.23

Table 3F shows optical specifications for the example single foldoptical system as illustrated in FIG. 6A. EFL is effective focal length,and Fno is the F-number of the optical system:

TABLE 3F EFL 15.37 Fno 3.0 semi-sensor diagonal 2.52 Macro distance 125cm

Tables 4A through 4F provide optical and physical characteristics forthe example single fold optical system as illustrated in FIG. 7A.

Table 4A shows all surface positions based on the Prism S1 globalcoordinate for the example single fold optical system as illustrated inFIG. 7A:

TABLE 4A x z angle (α) aperture 0 0.28 0 Prism S1 0.000 0.000 0 Prisminner surface 0.000 0.349 0 Prims S2 0.000 3.134 45 Prism S3 −2.7853.134 90 L1 S1 −4.220 3.134 90 L1S2 −5.265 3.134 90 L2S1 −5.518 3.134 90L2S2 −5.908 3.134 90 L3S1 −9.594 3.134 90 L3S2 −10.254 3.134 90 L4S1−10.995 3.134 90 L4S2 −12.095 3.134 90 IRcut S1 −13.946 3.134 90 IRcutS2 −14.156 3.134 90 image plane (INF) −14.256 3.134 90

Tables 4B through 4D show aspherical values for the surfaces of theoptical components for the example single fold optical system asillustrated in FIG. 7A:

TABLE 4B Prism S1 L1S1 L1S2 Radius of curvature 9.6677 −4.5962 24.13704th order −5.32525E−04 −4.96952E−03 −6.96106E−03 6th order −8.96273E−06 3.25426E−04  2.34753E−03 8th order  1.55564E−06 −2.59701E−05−5.13966E−04 10th order −1.69683E−07  3.54569E−05  1.47389E−04 12thorder  7.82692E−09 −7.43090E−06 −1.18246E−05 14th order  1.91989E−06 1.99593E−07

TABLE 4C L2S1 L2S2 L3S1 Radius of curvature −5.8392 −2.7004 7.9220 4thorder  2.08846E−02  2.80123E−02  4.36643E−02 6th order −6.99973E−03−1.15153E−02 −8.56777E−03 8th order  9.61573E−04  2.21425E−03 4.95687E−04 10th order −3.49028E−05 −6.01848E−04 −4.46371E−05 12thorder −8.47955E−07  1.40503E−04 14th order −2.38157E−06 −2.85205E−05

TABLE 4D L3S2 L4S1 L4S2 Radius of curvature −5.3114 −81.4716 6.5864 4thorder  3.90863E−02 −1.94553E−03  8.73233E−04 6th order −8.82724E−03 1.24447E−03 −2.40538E−04 8th order  1.21063E−03 −3.53784E−04 4.64840E−05 10th order −9.15778E−05  8.00536E−05 −2.44547E−06 12thorder −7.42994E−06  1.63492E−06 14th order  4.81112E−07 −3.05210E−08

Table 4E shows material characteristics of the optical components forthe example single fold optical system as illustrated in FIG. 7A. Ndrefers to refractive index, and Vd refers to Abbe number of thematerial. L1-L4 refer to the four lenses in the second lens group fromthe object side to the image side of the optical system:

TABLE 4E Prism L1 L2 L3 L4 Nd 1.514 1.834 1.544 1.671 1.544 Vd 51.3537.16 55.97 19.23 55.97

Table 4F shows optical specifications for the example single foldoptical system as illustrated in FIG. 7A. EFL is effective focal length,and Fno is the F-number of the optical system:

TABLE 4F EFL 15.3 Fno 3.0 semi-sensor diagonal 2.52 Macro distance 125cm

Tables 5A through 5F provide optical and physical characteristics forthe example single fold optical system as illustrated in FIG. 8A.

Table 5A shows all surface positions based on the Prism S1 globalcoordinate for the example single fold optical system as illustrated inFIG. 8A:

TABLE 5A x z angle (α) aperture 0 0.28 0 Prism S1 0.000 0.000 0 Prisminner surface 0.000 0.700 0 Prims S2 0.000 3.612 45 Prism S3 −2.9123.612 90 L1 S1 −4.177 3.612 90 L1S2 −5.222 3.612 90 L2S1 −5.475 3.612 90L2S2 −5.865 3.612 90 L3S1 −9.551 3.612 90 L3S2 −10.211 3.612 90 L4S1−10.952 3.612 90 L4S2 −12.052 3.612 90 IRcut S1 −13.792 3.612 90 IRcutS2 −14.002 3.612 90 image plane (INF) −14.102 3.612 90

Tables 5B through 5D show aspherical values for the surfaces of theoptical components for the example single fold optical system asillustrated in FIG. 8A:

TABLE 5B Prism S1 L1S1 L1S2 Radius of curvature 10.9936 −4.5962 24.13704th order −4.47670E−04 −4.96952E−03 −6.96106E−03 6th order −1.61255E−06 3.25426E−04  2.34753E−03 8th order −1.31071E−07 −2.59701E−05−5.13966E−04 10th order  3.27852E−08  3.54569E−05  1.47389E−04 12thorder −1.37757E−09 −7.43090E−06 −1.18246E−05 14th order  1.91989E−06 1.99593E−07

TABLE 5C L2S1 L2S2 L3S1 Radius of curvature −5.8392 −2.7004 7.9220 4thorder  2.08846E−02  2.80123E−02  4.36643E−02 6th order −6.99973E−03−1.15153E−02 −8.56777E−03 8th order  9.61573E−04  2.21425E−03 4.95687E−04 10th order −3.49028E−05 −6.01848E−04 −4.46371E−05 12thorder −8.47955E−07  1.40503E−04 14th order −2.38157E−06 −2.85205E−05

TABLE 5D L3S2 L4S1 L4S2 Radius of curvature −5.3114 −81.4716 6.5864 4thorder  3.90863E−02 −1.94553E−03  8.73233E−04 6th order −8.82724E−03 1.24447E−03 −2.40538E−04 8th order  1.21063E−03 −3.53784E−04 4.64840E−05 10th order −9.15778E−05  8.00536E−05 −2.44547E−06 12thorder −7.42994E−06  1.63492E−06 14th order  4.81112E−07 −3.05210E−08

Table 5E shows material characteristics of the optical components forthe example single fold optical system as illustrated in FIG. 8A. Ndrefers to refractive index, and Vd refers to Abbe number of thematerial. L1-L4 refer to the four lenses in the second lens group fromthe object side to the image side of the optical system:

TABLE 5E Prism L1 L2 L3 L4 Nd 1.583 1.834 1.544 1.671 1.544 Vd 59.3837.16 55.97 19.23 55.97

Table 5F shows optical specifications for the example single foldoptical system as illustrated in FIG. 8A. EFL is effective focal length,and Fno is the F-number of the optical system:

TABLE 5F EFL 15.3 Fno 3.0 semi-sensor diagonal 2.52 Macro distance 125cm

Tables 6A through 6F provide optical and physical characteristics forthe example single fold optical system as illustrated in FIG. 9A.

Table 6A shows all surface positions based on the Prism S1 globalcoordinate for the example single fold optical system as illustrated inFIG. 9A:

TABLE 6A x z angle (α) aperture 0 0.7 0 Prism S1 0.000 0.000 0 Prism S20.000 3.700 45 Prism S3 −3.300 3.700 90 L1 S1 −3.400 3.700 90 L1S2−3.992 3.700 90 L2S1 −4.092 3.700 90 L2S2 −4.488 3.700 90 L3S1 −8.2503.700 90 L3S4 −8.829 3.700 90 L4S1 −11.202 3.700 90 L4S2 −12.600 3.70090 IRcut S1 −13.990 3.700 90 IRcut S2 −14.200 3.700 90 image plane (INF)−14.300 3.700 90

Tables 6B through 6D show aspherical values for the surfaces of theoptical components for the example single fold optical system asillustrated in FIG. 9A:

TABLE 6B Prism S1 L1S1 L1S2 Radius of curvature 5.6321 −11.6936 21.59324th order −2.68374E−04 −2.40165E−03  −1.27735E−03 6th order −7.96206E−069.06400E−04  1.10220E−03 8th order  2.54679E−07 1.27434E−05 −1.35119E−0410th order −5.97297E−08 1.21772E−05  1.10012E−05 12th order  2.34852E−09−9.78359E−06   1.83952E−05 14th order 3.15343E−06 −1.67661E−06

TABLE 6C L2S1 L2S2 L3S1 Radius of curvature −298.9651 −4.7109 5.5578 4thorder 2.63966E−03 −1.33363E−03 −2.38091E−02 6th order −2.23391E−03 −2.71636E−03  1.24316E−02 8th order 3.72586E−04  4.30366E−04−1.91564E−03 10th order 9.73830E−05  2.05012E−04 −8.41607E−05 12th order−3.53637E−05  −1.05166E−04  1.12014E−04 14th order 3.18196E−06 1.25474E−05 −2.07762E−05

TABLE 6D L3S2 L4S1 L4S2 Radius of curvature −7.7071 −20.8157 7.0734 4thorder −2.99254E−02 −5.62662E−03 −7.04620E−04 6th order  1.16934E−02 1.10755E−04 −5.93634E−04 8th order −8.47579E−04 −6.24552E−05 2.81487E−05 10th order −3.95495E−04  2.98711E−05  4.61457E−06 12thorder  1.22802E−04 −4.10901E−06  1.30778E−07 14th order −1.28792E−05 2.54296E−07 −6.59262E−10

Table 6E shows material characteristics of the optical components forthe example single fold optical system as illustrated in FIG. 9A. Ndrefers to refractive index, and Vd refers to Abbe number of thematerial. L1-L4 refer to the four lenses in the second lens group fromthe object side to the image side of the optical system:

TABLE 6E Prism L1 L2 L3 L4 Nd 1.535 1.544 1.671 1.544 1.671 Vd 55.7355.97 19.23 55.97 19.23

Table 6F shows optical specifications for the example single foldoptical system as illustrated in FIG. 9A. EFL is effective focal length,and Fno is the F-number of the optical system:

TABLE 6F EFL 22.03 Fno 4.0 semi-sensor diagonal 2.268 Macro distance 175cm

Anamorphic Lenses in Folded Optical Systems

Folded optical systems such as the single fold optical systemsillustrated in FIGS. 1 through 11 include at least one prism with areflective, flat second surface to fold the optical axis of the opticalsystem. However, surface errors of the reflective surface of theprism(s) in folded optical systems may cause aberrations, in particularastigmatism, in the optical system. In other words, while ideallyperfectly flat, the reflective surface of the prism will typically beflat within some tolerance level (e.g., a few microns) of themanufacturing process. Thus, the second (reflective) surface may beslightly curved, which results in the aforementioned aberrations. Usinga glass prism may help to limit these aberrations when compared toplastic prisms, as glass can be polished to provide a tighter tolerancelevel in the manufacturing process than plastic. However, the reflectivesurface of a glass prism can only be guaranteed to be flat within sometolerance level. Further, due to variations in the manufacturingprocess, different groups or batches of prisms (whether glass orplastic) may vary in the “flatness” of the second, reflective surface.

In an optical system with astigmatism, rays that propagate in twoperpendicular planes have different foci. For example, if an opticalsystem with astigmatism is used to form an image of a cross, thevertical and horizontal lines will be in sharp focus at two differentdistances.

Embodiments of folded optical systems that include at least oneanamorphic lens that is configured and oriented to correct foraberrations including astigmatism caused by surface errors of thereflective surface of the prism(s) in the folded optical systems aredescribed. An anamorphic lens as described herein may, for example, beused in embodiments of the single fold optical systems that include asingle power prism as described in reference to FIGS. 1 through 11 .However, anamorphic lenses as described herein may also be used in othersingle fold optical systems or double fold optical systems to correctfor aberrations including astigmatism caused by surface errors of thereflective surface(s) of the prism(s) in the folded optical systems.Anamorphic lenses as described herein may be used to correct forastigmatism caused by the flat reflective surfaces of power prisms ortriangular prisms, or by the curved reflective surfaces of prisms suchas freeform prisms.

A spherical lens has one or two curved (concave or convex) surfaces. Thecurvature of the surface(s) is the same on all axes (e.g., on an X and Yaxis). Spherical lenses pass the image to the sensor without affectingthe aspect ratio. An anamorphic lens has at least one curved (convex orconcave) surface in which the curvature is different on at least oneaxis (e.g., different on the X axis than on the Y axis). The effectivesurface of an anamorphic lens may thus be oval, rather than round as intypical spherical lenses. Anamorphic lenses thus distort the image,squeezing it in one direction (e.g., horizontally) while leaving theother (e.g., vertical) aspect unaffected. Aspherical lenses can bedesigned and manufactured with different curvatures on different axes tocorrect for aberrations (e.g., astigmatism) caused by surface errors(e.g., curvature in one or more directions) of the reflective surfacesof prisms used in folded optical systems. In a folded telephoto opticalsystem, an anamorphic lens may be used to correct the astigmatism by upto 20 μm without creating a distortion problem, as the effect ondistortion of the anamorphic lens is relatively small.

The astigmatism caused by the reflective surface of prisms may differ.For example, one batch of prisms may have more, or less, surface errorand thus more, or less, astigmatism than another batch of prisms, or the“direction” of the astigmatism may be different. Thus, in embodiments,the anamorphic lens may be configured to be rotated 90 degrees tocorrect for differing astigmatism in different prisms. In addition, twoor more different anamorphic lenses with different amounts ororientations of curvature to correct for different levels of astigmatismmay be provided, and a correct anamorphic lens and orientation of thelens may be selected for use with one or more prisms. For example, oneanamorphic lens may be configured to correct for 2 micros ofastigmatism, another for 10 microns of astigmatism, another for 20microns of astigmatism, and so on.

A manufacturing process for folded optical systems that includeanamorphic lenses to correct for aberrations including astigmatismcaused by surface errors of the reflective surface(s) of the prism(s) isalso described.

FIGS. 12A through 12D illustrate using an anamorphic lens in a lensstack to correct aberrations including astigmatism caused by surfaceerrors of the reflective surface of a prism in a single fold opticalsystem, according to some embodiments. FIG. 12A shows an example singlefold lens system as shown in FIG. 1 that includes a power prism 1210with a reflective surface 1214. In this example, the second lens 1222 inthe lens stack 1220 has been replaced with an anamorphic lens as shownin FIGS. 12B and 12C to correct for astigmatism caused by surface errors(curvature) of the reflective surface 1214. FIGS. 12B and 12C show thatthe curvature of the second (object side) surface of the anamorphic lens1222 is different on the X axis than on the Y axis. To correct fordiffering astigmatism caused by the reflective surface 1214 of prism1210, the lens 1222 may be rotated 90 degrees. Alternatively, adifferent anamorphic lens 1222 with different curvature to correct for adifferent level of astigmatism may be selected and used with the prism1210.

While FIG. 12A shows an anamorphic lens as the second lens 1222 in lensstack 1220, an anamorphic lens may instead be used at other lenses inthe optical system 1200, for example as the first lens in the lens stack1220. In some embodiments, more than one anamorphic lens may be used inan optical system 1200.

FIG. 12D graphically illustrates correcting for astigmatism in anexample optical system 1200 with an anamorphic lens 1222 as illustratedin FIGS. 12A through 11C. (A)(0) shows an ideal MTF for the opticalsystem, (A)(1) shows MTF with +0.2 microns of astigmatism, and (A)(1)shows MTF with −0.2 microns of astigmatism. (B)(1) shows correction ofMTF with anamorphic lens 1122 oriented at azimuth 0 degrees to correctfor the astigmatism of (A)(1), and (B)(2) shows correction of MTF withanamorphic lens 1122 oriented at azimuth 90 degrees to correct for theastigmatism of (A)(2).

FIG. 13 illustrates using an anamorphic lens 1322 in a lens stack 1320to correct aberrations including astigmatism caused by surface errors ofthe reflective surface 1314 of a first prism 1310 in a double foldoptical system 1300 that includes two light folding elements (e.g., afirst and second prism, or a first prism and a mirror), according tosome embodiments. In this example, the second lens 1322 in the lensstack 1320 has been replaced with an anamorphic lens, for example asshown in FIGS. 11B and 11C, to correct for astigmatism caused by surfaceerrors (curvature) of the reflective surface 1314 of the first prism1310. To correct for differing astigmatism caused by the reflectivesurface 1314 of prism 1310, the lens 1322 may be rotated 90 degrees.Alternatively, a different anamorphic lens 1322 with different curvatureto correct for a different level of astigmatism may be selected and usedwith the prism 1310.

While FIG. 13 shows an anamorphic lens as the second lens 1322 in lensstack 1320, an anamorphic lens may instead be used at other lenses inthe optical system 1300, for example as the first lens in the lens stack1320. In some embodiments, more than one anamorphic lens may be used inan optical system 1300.

FIG. 14 illustrates using an anamorphic lens to correct aberrationsincluding astigmatism caused by a freeform prism, according to someembodiments. As previously mentioned, freeform optics involve opticaldesigns with at least one surface which has no translational orrotational symmetry about axes normal to the mean plane of the surface.A freeform prism is thus a prism that has at least one surface which hasno translational or rotational symmetry about axes normal to the meanplane of the surface. Example folded optical system 1400 includes, inorder from an object side to an image side, an anamorphic lens 1410, afirst freeform prism 1420, and a second freeform prism 1430. The opticalsystem 1400 may also include an aperture stop, for example locatedbetween anamorphic lens 1410 and freeform prism 1420. Light from anobject field is refracted by anamorphic lens 1410 to surface S1 offreeform prism 1420. The light is refracted by surface S1 to surface S2,which reflects the light back to surface S1, thus folding the opticalaxis once. Surface S1 reflects the light to surface S3, thus folding theoptical axis a second time. The light is refracted by surface S3 tosurface S4 of freeform prism 1430. Surface S4 refracts the light tosurface S5, which reflects the light to surface S6, thus folding theoptical axis a third time. Surface S6 reflects the light to surface S5,thus folding the optical axis a fourth time. Surface S5 refracts thelight received from surface S6 to form an image at an image plane, forexample at or near the surface of a sensor.

The optical system 1400 of FIG. 14 is given by way of example. Forexample, an optical system may include only one freeform prism, mayinclude a freeform prism and a standard prism or power prism, and/or mayinclude additional spherical, aspherical, or anamorphic lenses. In thisexample, anamorphic lens 1410 is configured correct for astigmatismcaused by one or more surfaces of the two freeform prisms, for exampleastigmatism caused by surface S2 of freeform prism 1420. To correct fordiffering astigmatism caused by the freeform prism(s), the anamorphiclens 1410 may be rotated 90 degrees. Alternatively, a differentanamorphic lens 1410 with different curvature to correct for a differentlevel of astigmatism may be selected and used with the freeformprism(s).

FIG. 15 is a high-level flowchart of a method of manufacturing a foldedoptical system that includes an anamorphic lens oriented to correct foraberrations including astigmatism caused by surface errors of thereflective surface of a prism in a folded optical system, according tosome embodiments. As indicated at 1500, optical performance of one ormore prisms may be measured to determine astigmatism caused by thereflective surface of the prism(s). Various methods may be used tomeasure the astigmatism of a prism, including but not limited to opticalmeasurement methods (e.g., to measure MTF of the prism) and physicalmeasurement methods (e.g., to directly measure surface error of thereflective surface). As indicated at 1510, an anamorphic lens may beselected according to the measured astigmatism of the prism(s). Aspreviously noted, different anamorphic lenses with different levels ofcorrection may be provided. As indicated at 1520, folded optical systemsincluding the prisms and lenses including the selected anamorphic lensoriented to correct for the measured astigmatism may be assembled. Aspreviously noted, an anamorphic lens may be rotated 90 degrees dependingon the measured astigmatism. This process may be repeated, for examplefor different batches of prisms.

Example Computing Device

FIG. 16 illustrates an example computing device, referred to as computersystem 3000, that may include or host embodiments of a camera with afolded optical system as illustrated in FIGS. 1 through 14 . Inaddition, computer system 3000 may implement methods for controllingoperations of the camera and/or for performing image processing ofimages captured with the camera. In different embodiments, computersystem 3000 may be any of various types of devices, including, but notlimited to, a personal computer system, desktop computer, laptop,notebook, tablet or pad device, slate, or netbook computer, mainframecomputer system, handheld computer, workstation, network computer, acamera, a set top box, a mobile device, a wireless phone, a smartphone,a consumer device, video game console, handheld video game device,application server, storage device, a television, a video recordingdevice, a peripheral device such as a switch, modem, router, or ingeneral any type of computing or electronic device.

In the illustrated embodiment, computer system 3000 includes one or moreprocessors 3010 coupled to a system memory 3020 via an input/output(I/O) interface 3030. Computer system 3000 further includes a networkinterface 3040 coupled to I/O interface 3030, and one or moreinput/output devices 3050, such as cursor control device 3060, keyboard3070, and display(s) 3080. Computer system 3000 may also include one ormore cameras 3090, for example at least one camera that includes asingle fold optical system as described above with respect to FIGS. 1through 14 .

In various embodiments, computer system 3000 may be a uniprocessorsystem including one processor 3010, or a multiprocessor systemincluding several processors 3010 (e.g., two, four, eight, or anothersuitable number). Processors 3010 may be any suitable processor capableof executing instructions. For example, in various embodimentsprocessors 3010 may be general-purpose or embedded processorsimplementing any of a variety of instruction set architectures (ISAs),such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitableISA. In multiprocessor systems, each of processors 3010 may commonly,but not necessarily, implement the same ISA.

System memory 3020 may be configured to store program instructions 3022and/or data 3032 accessible by processor 3010. In various embodiments,system memory 3020 may be implemented using any suitable memorytechnology, such as static random access memory (SRAM), synchronousdynamic RAM (SDRAM), nonvolatile/Flash-type memory, or any other type ofmemory. In the illustrated embodiment, program instructions 3022 may beconfigured to implement various interfaces, methods and/or data forcontrolling operations of camera 3090 and for capturing and processingimages with integrated camera 3090 or other methods or data, for exampleinterfaces and methods for capturing, displaying, processing, andstoring images captured with camera 3090. In some embodiments, programinstructions and/or data may be received, sent or stored upon differenttypes of computer-accessible media or on similar media separate fromsystem memory 3020 or computer system 3000.

In one embodiment, I/O interface 3030 may be configured to coordinateI/O traffic between processor 3010, system memory 3020, and anyperipheral devices in the device, including network interface 3040 orother peripheral interfaces, such as input/output devices 3050. In someembodiments, I/O interface 3030 may perform any necessary protocol,timing or other data transformations to convert data signals from onecomponent (e.g., system memory 3020) into a format suitable for use byanother component (e.g., processor 3010). In some embodiments, I/Ointerface 3030 may include support for devices attached through varioustypes of peripheral buses, such as a variant of the Peripheral ComponentInterconnect (PCI) bus standard or the Universal Serial Bus (USB)standard, for example. In some embodiments, the function of I/Ointerface 3030 may be split into two or more separate components, suchas a north bridge and a south bridge, for example. Also, in someembodiments some or all of the functionality of I/O interface 3030, suchas an interface to system memory 3020, may be incorporated directly intoprocessor 3010.

Network interface 3040 may be configured to allow data to be exchangedbetween computer system 3000 and other devices attached to a network3085 (e.g., carrier or agent devices) or between nodes of computersystem 3000. Network 3085 may in various embodiments include one or morenetworks including but not limited to Local Area Networks (LANs) (e.g.,an Ethernet or corporate network), Wide Area Networks (WANs) (e.g., theInternet), wireless data networks, some other electronic data network,or some combination thereof. In various embodiments, network interface3040 may support communication via wired or wireless general datanetworks, such as any suitable type of Ethernet network, for example;via telecommunications/telephony networks such as analog voice networksor digital fiber communications networks; via storage area networks suchas Fibre Channel SANs, or via any other suitable type of network and/orprotocol.

Input/output devices 3050 may, in some embodiments, include one or moredisplay terminals, keyboards, keypads, touchpads, scanning devices,voice or optical recognition devices, or any other devices suitable forentering or accessing data by computer system 3000. Multipleinput/output devices 3050 may be present in computer system 3000 or maybe distributed on various nodes of computer system 3000. In someembodiments, similar input/output devices may be separate from computersystem 3000 and may interact with one or more nodes of computer system3000 through a wired or wireless connection, such as over networkinterface 3040.

As shown in FIG. 16 , memory 3020 may include program instructions 3022,which may be processor-executable to implement any element or action tosupport integrated camera 3090, including but not limited to imageprocessing software and interface software for controlling camera(s)3090. In some embodiments, images captured by camera(s) 3090 may bestored to memory 3020. In addition, metadata for images captured bycamera(s) 3090 may be stored to memory 3020.

Those skilled in the art will appreciate that computer system 3000 ismerely illustrative and is not intended to limit the scope ofembodiments. In particular, the computer system and devices may includeany combination of hardware or software that can perform the indicatedfunctions, including computers, network devices, Internet appliances,PDAs, wireless phones, pagers, video or still cameras, etc. Computersystem 3000 may also be connected to other devices that are notillustrated, or instead may operate as a stand-alone system. Inaddition, the functionality provided by the illustrated components mayin some embodiments be combined in fewer components or distributed inadditional components. Similarly, in some embodiments, the functionalityof some of the illustrated components may not be provided and/or otheradditional functionality may be available.

Those skilled in the art will also appreciate that, while various itemsare illustrated as being stored in memory or on storage while beingused, these items or portions of them may be transferred between memoryand other storage devices for purposes of memory management and dataintegrity. Alternatively, in other embodiments some or all of thesoftware components may execute in memory on another device andcommunicate with the illustrated computer system 3000 via inter-computercommunication. Some or all of the system components or data structuresmay also be stored (e.g., as instructions or structured data) on acomputer-accessible medium or a portable article to be read by anappropriate drive, various examples of which are described above. Insome embodiments, instructions stored on a computer-accessible mediumseparate from computer system 3000 may be transmitted to computer system3000 via transmission media or signals such as electrical,electromagnetic, or digital signals, conveyed via a communication mediumsuch as a network and/or a wireless link. Various embodiments mayfurther include receiving, sending or storing instructions and/or dataimplemented in accordance with the foregoing description upon acomputer-accessible medium. Generally speaking, a computer-accessiblemedium may include a non-transitory, computer-readable storage medium ormemory medium such as magnetic or optical media, e.g., disk orDVD/CD-ROM, volatile or non-volatile media such as RAM (e.g. SDRAM, DDR,RDRAM, SRAM, etc.), ROM, etc. In some embodiments, a computer-accessiblemedium may include transmission media or signals such as electrical,electromagnetic, or digital signals, conveyed via a communication mediumsuch as network and/or a wireless link.

The methods described herein may be implemented in software, hardware,or a combination thereof, in different embodiments. In addition, theorder of the blocks of the methods may be changed, and various elementsmay be added, reordered, combined, omitted, modified, etc. Variousmodifications and changes may be made as would be obvious to a personskilled in the art having the benefit of this disclosure. The variousembodiments described herein are meant to be illustrative and notlimiting. Many variations, modifications, additions, and improvementsare possible. Accordingly, plural instances may be provided forcomponents described herein as a single instance. Boundaries betweenvarious components, operations and data stores are somewhat arbitrary,and particular operations are illustrated in the context of specificillustrative configurations. Other allocations of functionality areenvisioned and may fall within the scope of claims that follow. Finally,structures and functionality presented as discrete components in theexample configurations may be implemented as a combined structure orcomponent. These and other variations, modifications, additions, andimprovements may fall within the scope of embodiments as defined in theclaims that follow.

The following clauses describe various aspects of optical systems,cameras, and/or methods incorporating embodiments as described above.

Clause 1. An optical system, comprising:

-   -   in order from an object side of the optical system to an image        side of the optical system:        -   a first lens group comprising a power prism that includes a            first surface, a second surface, and a third surface on an            optical axis of the optical system, wherein the first            surface is a transmissive aspherical surface that provides            positive refractive power for the prism, wherein the second            surface is a reflective surface that folds the optical axis            of the optical system, and wherein the third surface is a            transmissive surface; and        -   a second lens group comprising two or more refractive            lenses; and    -   wherein the optical system satisfies the conditional expression:

0.6<B/A<2.3,

-   -   where A is power of the optical system, and B is power of the        first lens group.

Clause 2. The optical system as recited in clause 1, wherein the opticalsystem satisfies the conditional expression:

−0.2<CD<0.1,

-   -   where C is power of the second lens group, and D is length of        the second lens group.

Clause 3. The optical system as recited in clause 1, further comprisingan aperture stop located on the object side of the power prism.

Clause 4. The optical system as recited in clause 1, wherein the powerprism is formed of an optical plastic material.

Clause 5. The optical system as recited in clause 1, wherein the powerprism comprises a glass prism and a refractive lens composed of anoptical plastic material attached to an object side surface of the glassprism.

Clause 6. The optical system as recited in clause 1, wherein the powerprism comprises a glass prism and a refractive lens composed of anoptical glass material attached to an object side surface of the glassprism.

Clause 7. The optical system as recited in clause 1, wherein Z-height ofthe optical system is 7.3 millimeters or less.

Clause 8. The optical system as recited in clause 1, wherein X-length ofthe optical system is 18 millimeters or less.

Clause 9. The optical system as recited in clause 1, wherein the secondlens group consists of four refractive lens elements.

Clause 10. The optical system as recited in clause 9, wherein the fourrefractive lens elements comprise, in order from the object side of theoptical system to the image side of the optical system:

-   -   a first lens with positive refractive power,    -   a second lens with negative refractive power;    -   a third lens with negative refractive power; and    -   a fourth lens with positive refractive power.

Clause 11. The optical system as recited in clause 9, wherein a secondlens in the second lens group from the object side of the optical systemis an anamorphic lens configured to correct for astigmatism caused bythe second surface of the power prism.

Clause 12. The optical system as recited in clause 11, wherein thesecond lens is configured to be rotated 90 degrees to correct for adifferent amount of astigmatism caused by the second surface of thepower prism.

Clause 13. The optical system as recited in clause 9, wherein at leastone of the lenses in the second lens group is an anamorphic lensconfigured to correct for astigmatism caused by the second surface ofthe power prism.

Clause 14. The optical system as recited in clause 1, further comprisinga light folding element located on the image side of the second lensgroup and configured to fold the optical axis of the optical system asecond time, wherein a second lens in the second lens group from theobject side of the optical system is an anamorphic lens configured tocorrect for astigmatism caused by the second surface of the power prism.

Clause 15. A camera, comprising, in order from an object side of thecamera to an image side of the camera:

-   -   an optical system comprising:        -   a first lens group comprising a power prism that includes a            first surface, a second surface, and a third surface on an            optical axis of the optical system, wherein the first            surface is a transmissive aspherical surface that provides            positive refractive power for the prism, wherein the second            surface is a reflective surface that folds the optical axis            of the optical system, and wherein the third surface is a            transmissive surface; and        -   a second lens group comprising two or more refractive            lenses; and    -   an image sensor configured to capture light projected onto a        surface of the image sensor by the optical system;    -   wherein the optical system satisfies the conditional expression:

0.6<B/A<2.3, and

−0.2<CD<0.1,

-   -   where A is power of the optical system, B is power of the first        lens group, C is power of the second lens group, and D is length        of the second lens group.

Clause 16. The camera as recited in clause 15, wherein Z-height of theoptical system is 7.3 millimeters or less, and wherein X-length of theoptical system is 18 millimeters or less.

Clause 17. The camera as recited in clause 15, further comprising anaperture stop located on the object side of the power prism.

Clause 18. The camera as recited in clause 15, further comprising aninfrared filter located between the second lens group and the imagesensor.

Clause 19. The camera as recited in clause 15, wherein at least one ofthe lenses in the second lens group is an anamorphic lens configured tocorrect for astigmatism caused by the second surface of the power prism.

Clause 20. An optical system, comprising:

-   -   a prism that includes a first surface, a second surface, and a        third surface on an optical axis of the optical system, wherein        the second surface is a reflective surface that folds the        optical axis of the optical system and the third surface is a        transmissive surface; and    -   one or more refractive lenses, wherein at least one of the one        or more refractive lenses is an anamorphic lens configured to        correct for astigmatism caused by the prism.

Clause 21. The optical system as recited in clause 20, wherein the firstsurface of the prism is a transmissive aspherical surface.

Clause 22. The optical system as recited in clause 20, wherein theanamorphic lens is configured to be rotated 90 degrees to correct for adifferent amount of astigmatism caused by the prism.

Clause 23. The optical system as recited in clause 20, wherein theoptical system comprises four refractive lenses located on an image sideof the prism, wherein a second lens of the four refractive lenses froman object side of the optical system is the anamorphic lens configuredto correct for astigmatism caused by the prism.

Clause 24. The optical system as recited in clause 23, wherein thesecond lens is configured to be rotated 90 degrees to correct for adifferent amount of astigmatism caused by the prism.

Clause 25. The optical system as recited in clause 20, wherein the oneor more refractive lenses are located on an image side of the prism, theoptical system further comprising a light folding element located on theimage side of the one or more lenses and configured to fold the opticalaxis of the optical system a second time.

Clause 26. The optical system as recited in clause 20, wherein the prismis a power prism with positive refractive power.

Clause 27. The optical system as recited in clause 20, furthercomprising a refractive lens with positive refractive power attached toan object side surface of the prism.

Clause 28. The optical system as recited in clause 20, furthercomprising an aperture stop located on an object side of the prism.

Clause 29. The optical system as recited in clause 20, wherein the prismis a freeform prism.

Clause 30. The optical system as recited in clause 29, wherein theoptical system further comprises a second freeform prism

Clause 31. The optical system as recited in clause 20, wherein theanamorphic lens is located on an object side of the prism.

Clause 32. The optical system as recited in clause 20, wherein theanamorphic lens is located on an image side of the prism.

Clause 33. A camera, comprising, in order from an object side of thecamera to an image side of the camera:

-   -   an optical system comprising:        -   a prism that includes a first surface, a second surface, and            a third surface on an optical axis of the optical system,            wherein the second surface is a reflective surface that            folds the optical axis of the optical system, and the third            surface is a transmissive surface; and        -   one or more refractive lenses, wherein at least one of the            one or more refractive lenses is an anamorphic lens            configured to correct for astigmatism caused by the prism;            and    -   an image sensor configured to capture light projected onto a        surface of the image sensor by the optical system.

Clause 34. The camera as recited in clause 33, wherein the first surfaceof the prism is a transmissive aspherical surface.

Clause 35. The camera as recited in clause 33, wherein the opticalsystem comprises four refractive lenses located on an image side of theprism, wherein a second lens of the four refractive lenses from theobject side of the optical system is the anamorphic lens configured tocorrect for astigmatism caused by the prism, and wherein the second lensis configured to be rotated 90 degrees to correct for a different amountof astigmatism caused by the prism.

Clause 36. The camera as recited in clause 33, further comprising alight folding element located between the four refractive lenses and theimage sensor and configured to fold the optical axis of the opticalsystem a second time.

Clause 37. The camera as recited in clause 33, further comprising anaperture stop located on the object side of the prism.

Clause 38. The camera as recited in clause 33, further comprising aninfrared filter located between the lens group and the image sensor.

Clause 39. The camera as recited in clause 33, wherein the prism is apower prism with positive refractive power.

Clause 40. The camera as recited in clause 33, wherein the prism is afreeform prism.

Clause 41. The camera as recited in clause 40, wherein the opticalsystem further comprises a second freeform prism

Clause 42. The camera as recited in clause 33, wherein the anamorphiclens is located on an object side of the prism.

Clause 43. The camera as recited in clause 33, wherein the anamorphiclens is located on an image side of the prism.

Clause 44. A method, comprising:

-   -   forming one or more prisms of an optical glass or plastic        material, wherein each prism includes a first surface, a second        reflective surface, and a third transmissive surface on an        optical axis;    -   measuring optical performance of the one or more prisms to        determine astigmatism caused by the prisms;    -   selecting one or more anamorphic lenses according to the        determined astigmatism of the one or more prisms; and assembling        one or more optical systems, each optical system including:        -   a first lens group including the prism; and        -   a second lens group including one or more refractive lens            elements, wherein at least one of the one or more refractive            lens elements is an anamorphic lens oriented to correct for            the determined astigmatism of the respective prism.

Clause 45. The method as recited in clause 44, wherein the opticalsystem further includes a second prism located on an image side of thesecond lens group.

Clause 46. The method as recited in clause 44, wherein the prism is apower prism.

Clause 47. The method as recited in clause 45, wherein the prism is afreeform prism.

1.-20. (canceled)
 21. An optical system, comprising: in order from anobject side of the optical system to an image side of the opticalsystem: a first lens group comprising a power prism that includes afirst surface, a second surface, and a third surface on an optical axisof the optical system, wherein the first surface is a transmissiveaspherical surface that provides positive refractive power for theprism, wherein the second surface is a reflective surface that folds theoptical axis of the optical system, and wherein the third surface is atransmissive surface; and a second lens group comprising in order fromthe object side to the image side: a first lens with positive refractivepower, a second lens with negative refractive power; a third lens withnegative refractive power; and a fourth lens with positive refractivepower; and wherein the optical system satisfies the conditionalexpression:0.6<B/A<2.3, where A is power of the optical system, and B is power ofthe first lens group.
 22. The optical system as recited in claim 21,wherein the optical system satisfies the conditional expression:−0.2<CD<0.1, where C is power of the second lens group, and D is lengthof the second lens group.
 23. The optical system as recited in claim 21,further comprising an aperture stop located on the object side of thepower prism.
 24. The optical system as recited in claim 21, wherein thepower prism is formed of an optical plastic material.
 25. The opticalsystem as recited in claim 21, wherein the power prism comprises a glassprism and a refractive lens composed of an optical plastic materialattached to an object side surface of the glass prism.
 26. The opticalsystem as recited in claim 21, wherein the power prism comprises a glassprism and a refractive lens composed of an optical glass materialattached to an object side surface of the glass prism.
 27. The opticalsystem as recited in claim 21, wherein Z-height of the optical system is7.3 millimeters or less.
 28. The optical system as recited in claim 21,wherein X-length of the optical system is 18 millimeters or less. 29.The optical system as recited in claim 21, wherein the second lens groupconsists of four refractive lens elements.
 30. The optical system asrecited in claim 21, wherein the second lens in the second lens group isan anamorphic lens configured to correct for astigmatism caused by thesecond surface of the power prism.
 31. The optical system as recited inclaim 30, wherein the second lens is configured to be rotated 90 degreesto correct for a different amount of astigmatism caused by the secondsurface of the power prism.
 32. The optical system as recited in claim21, wherein at least one of the lenses in the second lens group is ananamorphic lens configured to correct for astigmatism caused by thesecond surface of the power prism.
 33. The optical system as recited inclaim 21, further comprising a light folding element located on theimage side of the second lens group and configured to fold the opticalaxis of the optical system a second time, wherein the second lens in thesecond lens group from the object side is an anamorphic lens configuredto correct for astigmatism caused by the second surface of the powerprism.
 34. A camera, comprising, in order from an object side of thecamera to an image side of the camera: an optical system comprising inorder from an object side of the optical system to an image side of theoptical system: a first lens group comprising a power prism thatincludes a first surface, a second surface, and a third surface on anoptical axis of the optical system, wherein the first surface is atransmissive aspherical surface that provides positive refractive powerfor the prism, wherein the second surface is a reflective surface thatfolds the optical axis of the optical system, and wherein the thirdsurface is a transmissive surface; and a second lens group comprisingtwo or more refractive lenses, wherein at least one of the lenses in thesecond lens group is an anamorphic lens configured to correct forastigmatism caused by the power prism; and wherein the optical systemsatisfies the conditional expression:0.6<B/A<2.3, where A is power of the optical system, and B is power ofthe first lens group.
 35. The camera as recited in claim 34, wherein theoptical system satisfies the conditional expression:−0.2<CD<0.1, where C is power of the second lens group, and D is lengthof the second lens group
 36. The camera as recited in claim 34, whereinZ-height of the optical system is 7.3 millimeters or less, and whereinX-length of the optical system is 18 millimeters or less.
 37. The cameraas recited in claim 34, further comprising an aperture stop located onthe object side of the power prism.
 38. The camera as recited in claim34, further comprising an infrared filter located between the secondlens group and the image sensor.
 39. The camera as recited in claim 34,wherein the second lens group consists of four refractive lens elements.40. The camera as recited in claim 34, further comprising a lightfolding element located on the image side of the second lens group andconfigured to fold the optical axis of the optical system a second time.